1. Field of the Invention
This invention concerns the treatment of cyanide-containing mining effluents, and more particularly relates to the recovery of gold from such effluents for economic value and removal of other metals for reasons of environmental protection.
2. Description of the Prior Art
The predominant method for mining gold involves the treatment of powdered gold-containing ore with an alkaline cyanide solution which dissolves finely divided gold particles dispersed within the ore. The resultant gold-containing aqueous cyanide solution is subsequently treated by way of electrolysis or precipitation techniques to recover the gold in metallic form.
In the course of such operations, a residual cyanide solution is produced as a “tailings” stream which contains trace amounts of gold in the form of aurocyanide anion, and other metals such as copper, silver, cadmium and nickel in the form of anionic cyanide complexes. The tailings are usually routed to an above-ground pond which functions as a long-term depository. Such tailings ponds are extremely toxic because of their high content of toxic heavy metal compounds and free cyanide.
Although the free cyanide can be destroyed by oxidizing agents such as chlorine and peroxide and long term exposure to air, the heavy metals remain as dissolved species in the pond. The ponds typically have a pH in the range of 8-10 and usually contain 2-10 parts per million (ppm) copper, 0.5 to 4 ppm gold, and other metals in concentration ranges of 2-10 ppm. Because of the high alkalinity of the water, and the complexity of its content, traditional metal removal technologies such as precipitation, electrolysis, and ion exchange have been technically unsuccessful or uneconomical. A primary challenge has been to selectively abstract the gold amidst the several other metal species present.
It is accordingly an object of the present invention to remove dissolved metals from cyanide-containing mine effluents.
It is a further object of this invention to provide a process whereby dissolved metals, particularly gold can be separately isolated from cyanide tailings ponds.
It is another object of the present invention to provide a process of the aforesaid nature which can economically reduce the toxicity hazard of a cyanide tailings pond.
These objects and other objects and advantages of the invention will be apparent from the following description.